Wireless Local Area Networks (“WLANs”) initially became popular for providing network access to Mobile Units such as laptop computers and PDAs. Recently, WLANs have been used to provide telecommunications services, i.e., with cellular phones being the Mobile Units. Support for voice communications has altered the requirements of WLAN equipment.
Because mobile units are typically powered by rechargeable batteries, it is generally desirable to conserve power in order to achieve the greatest practical operating time from a battery charge. There is a particularly keen focus on power conservation in cell phone engineering, perhaps because cell phones are expected to operate for longer periods of time between battery charges in comparison with other types of Mobile Units. One technique for conserving battery power is sleep mode. Sleep mode is a technique in which non-essential Mobile Unit functions are temporarily halted, and non-essential Mobile Unit components are temporarily de-powered. A Mobile Unit typically signals to the associated Access Point prior to entering sleep mode in order to indicate the planned duration of the sleep mode. The sleep mode duration signaled by the Mobile Unit is known as a “Listen Interval,” and it is measured in terms of a number of beacons. The Access Point must then buffer traffic bound for the Mobile Unit in sleep mode. In particular, the IEEE 802.11 standard mandates that the traffic be buffered for at least the Listen Interval. An aging function is employed by the Access Point to determine how long traffic has been buffered in order to prompt optional discard of traffic that is buffered beyond the Listen Interval. The extent to which traffic is buffered beyond the Listen Interval is generally at the discretion of the equipment designer. While the sleep mode technique facilitates Mobile Unit battery power savings, it is somewhat problematic because the memory required to buffer traffic in the Access Point increases the cost of the Access Point, and it is particularly desirable to reduce the cost of Access Points because they are logically disposed at the network edge and therefore deployed in relatively large numbers.